WO2014102932A1

WO2014102932A1 - Exhaust purification system for internal combustion engine

Info

Publication number: WO2014102932A1
Application number: PCT/JP2012/083659
Authority: WO
Inventors: 見上　晃; 中山　茂樹; 大橋　伸基; 高田　圭; 櫻井　健治; 佳久塚本; 寛大月; 潤一松尾; 山本　一郎
Original assignee: トヨタ自動車株式会社
Priority date: 2012-12-26
Filing date: 2012-12-26
Publication date: 2014-07-03
Also published as: CN104870767A; EP2940265A1; JPWO2014102932A1; US20150330275A1; EP2940265A4

Abstract

The objective of the present invention is to prevent a decrease in the NOx purification rate in conjunction with a filter regeneration process in an exhaust purification system for an internal combustion engine equipped with a filter supporting an SCR catalyst. In the present invention, after execution of the filter regeneration process is completed the temperature of the exhaust discharged from the internal combustion engine is increased, thereby increasing the filter temperature and removing hydrocarbons adhering to the filter.

Description

Exhaust gas purification system for internal combustion engine

The present invention relates to an exhaust gas purification system for an internal combustion engine.

2. Description of the Related Art Conventionally, an exhaust purification device provided in an exhaust passage of an internal combustion engine has been developed in which a filter carries a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst). The filter collects particulate matter (hereinafter referred to as PM) in the exhaust. The SCR catalyst reduces NOx in the exhaust gas using ammonia (NH ₃ ) as a reducing agent. Hereinafter, a filter carrying such an SCR catalyst may be referred to as SCRF.

By adopting SCRF as the exhaust gas purification device, the size of the exhaust gas purification device can be made smaller than when the filter and the SCR catalyst are separately provided in the exhaust passage. Therefore, the mountability of the exhaust purification device can be improved. Further, by adopting SCRF, it becomes possible to arrange the SCR catalyst upstream of the exhaust passage. The more upstream the SCR catalyst is arranged in the exhaust passage, the more easily the SCR catalyst is heated by the heat of the exhaust. Therefore, it is possible to improve the warm-up property of the SCR catalyst and improve the NOx purification rate (the ratio of the NOx amount reduced in the SCR catalyst to the NOx amount flowing into the SCRF) in the SCR catalyst.

Patent Document 1 discloses a configuration in which an oxidation catalyst, an injector, an SCRF, and a slip oxidation catalyst are sequentially provided from the upstream side along the flow of exhaust gas in an exhaust passage of a diesel engine. An injector is a device that injects ammonia or a precursor of ammonia into the exhaust. The slip oxidation catalyst is a catalyst that oxidizes ammonia that has passed through the SCRF.

Here, the collected PM is deposited on the SCRF. Therefore, filter regeneration processing is executed in an exhaust purification system equipped with SCRF. The filter regeneration process is a process for oxidizing and depositing PM deposited on the SCRF. The filter regeneration process is realized by supplying fuel to a pre-stage catalyst having an oxidation function provided in an exhaust passage upstream of SCRF. When the fuel is oxidized in the pre-stage catalyst, the exhaust gas flowing into the SCRF is heated by the oxidation heat. Therefore, the temperature of SCRF can be raised to the filter regeneration temperature at which PM oxidation is promoted.

Patent Document 2 discloses a technique for reducing the amount of ammonia supplied to the SCRF before heat regeneration (filter regeneration) of the SCRF. According to this, the amount of ammonia adsorbed on the SCR catalyst can be reduced before the thermal regeneration of the SCRF. As a result, it is possible to suppress the release of ammonia accompanying the thermal regeneration of SCRF.

Further, Patent Document 3 estimates the amount of HC attached to the SCR catalyst provided in the exhaust passage, and raises the temperature of the SCR catalyst when the amount of HC attached exceeds the allowable amount of attachment. A technique for desorbing HC is disclosed. Further, Patent Document 2 discloses a technique for stopping the temperature increase of the SCR catalyst when the amount of HC adhering to the SCR catalyst decreases to a predetermined lower limit after the temperature increase of the SCR catalyst is started.

Special table 2007-501353 gazette JP 2007-170388 A JP 2009-41437 A

SCRF is supplied with ammonia or an ammonia precursor. Then, in the SCR catalyst carried on the SCRF, NOx in the exhaust is reduced using ammonia as a reducing agent. Here, when ammonia is oxidized, NOx may be generated. Since it is necessary to suppress the generation of such NOx, it is difficult to carry a catalyst having a high oxidation ability on SCRF. Therefore, the SCR catalyst supported on SCRF has very low oxidation ability.

When the filter regeneration process as described above is executed, a part of the HC contained in the fuel supplied to the pre-stage catalyst may pass through the pre-stage catalyst without being oxidized in the pre-stage catalyst. HC that has passed through the front catalyst flows into SCRF. As described above, the SCR catalyst supported on SCRF has a very low oxidation ability. Therefore, when HC flows into SCRF, a part of the HC adheres to SCRF. Then, there is a possibility that the attached HC is not oxidized but remains attached to the SCRF.

When HC adheres to the SCRF, the ammonia adsorption site to which ammonia should be adsorbed in the SCR catalyst supported on the SCRF is blocked by the HC. When the ammonia adsorption site is blocked by HC, it becomes difficult for ammonia to be adsorbed on the SCR catalyst after the completion of the filter regeneration process. As a result, the NOx purification rate in the SCR catalyst decreases.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress a decrease in the NOx purification rate accompanying the execution of the filter regeneration process in an exhaust gas purification system for an internal combustion engine equipped with an SCRF.

In the present invention, after the completion of the filter regeneration processing, the temperature of the SCRF is raised by raising the temperature of the exhaust gas discharged from the internal combustion engine, thereby removing HC adhering to the SCRF.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
A pre-stage catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
A fuel supply device for supplying fuel to the upstream catalyst;
A filter that is provided in an exhaust passage downstream of the preceding catalyst and collects particulate matter in exhaust gas, and carries a selective reduction type NOx catalyst that reduces NOx in exhaust gas using ammonia as a reducing agent. (SCRF),
An ammonia supply device for supplying ammonia or an ammonia precursor to the filter;
A filter regeneration process execution unit for performing a filter regeneration process for increasing the temperature of the filter by supplying fuel from the fuel supply device to the upstream catalyst, thereby removing particulate matter deposited on the filter;
After the completion of the filter regeneration process by the filter regeneration process execution unit, the temperature of the filter is raised by raising the temperature of the exhaust discharged from the internal combustion engine, thereby removing the HC adhering to the filter. An HC poisoning recovery process execution unit that executes a poison recovery process.

When the temperature of the SCRF is raised by raising the temperature of the exhaust gas discharged from the internal combustion engine, the temperature of the SCRF can be raised while suppressing an increase in the amount of HC flowing into the SCRF. Therefore, by executing the HC poisoning recovery process after the completion of the filter regeneration process, it is possible to remove HC adhering to the SCRF by executing the filter regeneration process while suppressing the attachment of new HC to the SCRF. it can.

Thereby, it can be prevented that the ammonia adsorption site in the SCR catalyst supported on the SCRF is blocked by the HC adhering thereto. Therefore, according to the present invention, it is possible to suppress a decrease in the NOx purification rate accompanying the execution of the filter regeneration process.

In the present invention, the HC poisoning recovery process may be executed for a time corresponding to the amount of HC adhering to the SCRF at the start of execution of the HC poisoning recovery process. The HC poisoning recovery process may be executed for a time corresponding to the execution time of the filter regeneration process. According to these, it is possible to suppress the HC poisoning recovery processing from being excessively long while sufficiently removing the HC adhering to the SCRF.

In the present invention, ammonia or an ammonia precursor in an amount corresponding to the SCRF temperature may be supplied to the SCRF by the ammonia supply device until the SCRF temperature reaches the target temperature during the filter regeneration process. .

According to this, ammonia can be adsorbed on the ammonia adsorption site in the SCR catalyst even during the time that the SCRF temperature reaches the target temperature during the execution of the filter regeneration process. Therefore, the amount of HC adsorbed on the SCRF during the filter regeneration process can be suppressed. Therefore, the execution time of the HC poisoning recovery process can be shortened.

According to the present invention, in the exhaust gas purification system for an internal combustion engine equipped with SCRF, it is possible to suppress a decrease in the NOx purification rate accompanying the execution of the filter regeneration process.

1 is a diagram illustrating a schematic configuration of an intake / exhaust system of an internal combustion engine according to Embodiment 1. FIG. 3 is a flowchart illustrating a flow of filter regeneration processing and HC poisoning recovery processing according to the first embodiment. SCRF temperature Tf, pre-catalyst temperature Tpc, fuel addition amount Fadd from the fuel addition valve, post-injection amount Fpost in the internal combustion engine, SCRF when the filter regeneration process and the HC poisoning recovery process according to the first embodiment are executed 6 is a time chart showing transitions of the HC adhesion amount Qhc, the ammonia gas addition amount Aadd from the ammonia addition valve, and the ammonia adsorption amount Qam on the SCR catalyst. 6 is a flowchart showing a flow of filter regeneration processing and HC poisoning recovery processing according to a modification of the first embodiment. 12 is a flowchart illustrating a flow of ammonia gas addition control during the execution of the filter regeneration process according to the second embodiment. SCRF temperature Tf, pre-catalyst catalyst temperature Tpc, fuel addition amount Fadd from the fuel addition valve, post-injection amount Fpost in the internal combustion engine, SCRF when the filter regeneration process and the HC poisoning recovery process according to the second embodiment are executed 6 is a time chart showing transitions of the HC adhesion amount Qhc, the ammonia gas addition amount Aadd from the ammonia addition valve, and the ammonia adsorption amount Qam on the SCR catalyst.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
Here, the case where the exhaust gas purification system for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described. However, the internal combustion engine according to the present invention is not limited to a diesel engine, and may be a gasoline engine or the like.

[Schematic configuration of intake and exhaust system]
FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. An air flow meter 11 is provided in the intake passage 2. The air flow meter 11 detects the intake air amount of the internal combustion engine 1.

In the exhaust passage 3, a first exhaust temperature sensor 12, a fuel addition valve 4, a front catalyst 5, an ammonia addition valve 6, SCRF 7, a second exhaust temperature sensor 13, a rear catalyst 8, and a third exhaust temperature sensor 14 are exhausted. It is provided in order from the upstream side along the flow.

The pre-stage catalyst 5 is an oxidation catalyst. However, the pre-stage catalyst 5 may be a catalyst other than the oxidation catalyst as long as it has an oxidation function. The fuel addition valve 4 adds fuel into the exhaust gas in order to supply fuel to the front catalyst 5.

In this embodiment, the fuel addition valve 4 corresponds to the fuel supply apparatus according to the present invention. However, in the internal combustion engine 1 without providing the fuel addition valve 4, the timing is later than the main fuel injection, and the injected fuel is not burned in the combustion chamber and is not burned in the exhaust passage 3. By executing the auxiliary fuel injection at the timing of discharging at the step, fuel can be supplied to the pre-stage catalyst 5.

SCRF7 is configured by supporting an SCR catalyst 7a on a wall flow type filter that collects PM in exhaust gas. The SCR catalyst 7a reduces NOx in the exhaust gas using ammonia as a reducing agent. The ammonia addition valve 6 adds ammonia gas into the exhaust gas so as to supply ammonia to the SCRF 7. When ammonia is supplied to the SCRF 7, the ammonia is once adsorbed at an ammonia adsorption site in the SCR catalyst 7a supported on the SCRF 7. Then, the adsorbed ammonia becomes a reducing agent, and NOx in the exhaust is reduced.

In addition, when ammonia is oxidized, NOx may be generated. Since it is necessary to suppress the generation of such NOx, the SCR catalyst 7a supported on the SCRF 7 has a very low oxidation ability.

In this embodiment, the ammonia addition valve 6 corresponds to the ammonia supply device according to the present invention. However, the ammonia supply device according to the present invention may be a device that supplies ammonia as a liquid or a solid. Further, the ammonia supply apparatus according to the present invention may be an apparatus for supplying an ammonia precursor. For example, in this embodiment, instead of the ammonia addition valve 6, a urea addition valve for adding an aqueous urea solution into the exhaust gas may be provided. In this case, urea is supplied to SCRF 7 as an ammonia precursor. And ammonia is produced | generated by urea hydrolyzing.

The latter stage catalyst 8 is an oxidation catalyst. However, the rear catalyst 8 may be another catalyst having an oxidation function. Further, the rear catalyst 8 may be a catalyst configured by combining an oxidation catalyst and an SCR catalyst that reduces ammonia in exhaust using ammonia as a reducing agent. In this case, for example, an oxidation catalyst is formed by supporting a noble metal such as platinum (Pt) on a support made of aluminum oxide (Al ₂ O ₃ ), zeolite, or the like, and copper (Cu SCR catalyst may be formed by supporting a base metal such as iron or iron (Fe). By making the rear catalyst 8 a catalyst having such a configuration, HC, CO and ammonia in the exhaust can be oxidized, and further, a part of ammonia is oxidized and NOx is generated and generated. NOx can be reduced using excess ammonia as a reducing agent.

The first exhaust temperature sensor 12, the second exhaust temperature sensor 13, and the third exhaust temperature sensor 14 are sensors that detect the temperature of the exhaust. The first exhaust temperature sensor 12 detects the temperature of the exhaust discharged from the internal combustion engine 1. The second exhaust temperature sensor 13 detects the temperature of the exhaust gas flowing out from the SCRF 7. The third exhaust temperature sensor 14 detects the temperature of the exhaust gas flowing out from the rear catalyst 8.

The internal combustion engine 1 is provided with an electronic control unit (ECU) 10. Various sensors such as an air flow meter 11, a first exhaust temperature sensor 12, a second exhaust temperature sensor 13, and a third exhaust temperature sensor 14 are electrically connected to the ECU 10. And the output signal of various sensors is input into ECU10. The ECU 10 estimates the flow rate of the exhaust gas in the exhaust passage 3 based on the output value of the air flow meter 11. Further, the ECU 10 estimates the temperature of the SCRF 7 based on the output value of the second exhaust temperature sensor 13 and estimates the temperature of the rear catalyst 8 based on the output value of the third exhaust temperature sensor 14.

Furthermore, the ECU 10 is electrically connected to the fuel injection valve, the fuel addition valve 4 and the ammonia addition valve 6 of the internal combustion engine 1. These devices are controlled by the ECU 10.

[Filter regeneration processing]
The collected PM is gradually deposited on the SCRF 7. Therefore, in this embodiment, a filter regeneration process is executed to remove PM deposited on the SCRF 7. The filter regeneration process according to the present embodiment is realized by adding fuel from the fuel addition valve 4 and supplying the fuel to the front catalyst 5 thereby. When the fuel is oxidized in the front catalyst 5, oxidation heat is generated. The exhaust gas flowing into the SCRF 7 is heated by this oxidation heat. Thereby, the temperature of SCRF7 rises. At the time of executing the filter regeneration process, the amount of fuel added from the fuel addition valve 4 is controlled to raise the temperature of the SCRF 7 to a predetermined filter regeneration temperature (for example, 650 ° C.) at which PM oxidation is promoted. As a result, PM deposited on SCRF 7 is oxidized and removed.

In this embodiment, the filter regeneration process is executed every time a predetermined time elapses. Note that the filter regeneration process may be executed each time a vehicle equipped with the internal combustion engine 1 travels a predetermined travel distance. Further, the filter regeneration process may be executed every time the PM accumulation amount in SCRF 7 reaches a predetermined accumulation amount. The PM accumulation amount in the SCRF 7 can be estimated based on the history of the fuel injection amount in the internal combustion engine 1, the flow rate of the exhaust gas flowing into the SCRF 7, the temperature of the SCRF 7, and the like.

When the filter regeneration process as described above is executed, a part of the HC contained in the fuel supplied to the front catalyst 5 may pass through the front catalyst 5 without being oxidized in the front catalyst 5. HC that has passed through the front catalyst 5 flows into the SCRF 7. Here, as described above, the SCR catalyst 7a supported on the SCRF 7 has a very low oxidizing ability. Therefore, when HC flows into SCRF7, a part of the HC adheres to SCRF7. Then, there is a possibility that the attached HC is not oxidized but remains attached to the SCRF. When HC adheres to the SCRF 7, the ammonia adsorption site to which ammonia should be adsorbed in the SCR catalyst 7a supported on the SCRF 7 is blocked by the HC. When the ammonia adsorption site is blocked by HC, it becomes difficult for ammonia to be adsorbed to the SCR catalyst 7a after the completion of the filter regeneration process. As a result, the NOx purification rate in the SCR catalyst 7a decreases.

Therefore, in this embodiment, after the completion of the filter regeneration process, the HC poisoning recovery process is executed to remove the HC adhering to the SCRF 7. The HC poisoning recovery process is a process of increasing the temperature of the SCRF 7 to an HC poisoning recovery temperature (for example, 650 ° C.) at which HC oxidation is promoted by increasing the temperature of the exhaust gas discharged from the internal combustion engine 1. . This HC poisoning recovery process is realized in the internal combustion engine 1 by executing the auxiliary fuel injection at a timing later than the main fuel injection and when the injected fuel is used for combustion in the combustion chamber. The By executing the auxiliary fuel injection at such timing, the temperature of the exhaust gas discharged from the internal combustion engine 1 can be raised. Hereinafter, the auxiliary fuel injection executed at such timing is referred to as post injection.

When the temperature of the SCRF 7 is increased by increasing the temperature of the exhaust gas discharged from the internal combustion engine 1, the temperature of the SCRF 7 can be increased while suppressing an increase in the amount of HC flowing into the SCRF 7. Therefore, by executing the HC poisoning recovery process after the completion of the filter regeneration process, it is possible to remove the HC adhering to the SCRF 7 by executing the filter regeneration process while suppressing the adhesion of new HC to the SCRF 7. it can.

Thereby, it can be prevented that the ammonia adsorption site in the SCR catalyst 7a supported on the SCRF 7 is blocked by the HC adhering thereto. Therefore, it is suppressed that HC inhibits the adsorption of ammonia, which is a reducing agent when reducing NOx, to the SCR catalyst 7a. Therefore, by performing the HC poisoning recovery process after the completion of the filter regeneration process, it is possible to suppress a decrease in the NOx purification rate associated with the execution of the filter regeneration process.

[Processing flow]
FIG. 2 is a flowchart showing the flow of the filter regeneration process and the HC poisoning recovery process according to this embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10.

In this flow, first, in step S101, it is determined whether or not an execution condition for the filter regeneration process is satisfied. In this embodiment, when a predetermined time has elapsed since the previous execution of the filter regeneration process has been completed, it is determined that the condition for executing the filter regeneration process has been satisfied. If a negative determination is made in step S101, the execution of this flow is temporarily terminated. On the other hand, when an affirmative determination is made in step S101, the process of step S102 is executed next.

In step S102, fuel addition from the fuel addition valve 4 is executed. That is, the filter regeneration process is executed. In the filter regeneration process, the temperature of the SCRF 7 is adjusted to the filter regeneration temperature, which is the target temperature, by controlling the amount of fuel added from the fuel addition valve 4.

Next, in step S103, it is determined whether or not an execution end condition for the filter regeneration process is satisfied. In the present embodiment, when a predetermined regeneration execution time has elapsed since the start of the execution of the filter regeneration process, it is determined that the execution end condition for the filter regeneration process is satisfied.

If a negative determination is made in step S103, the processes in steps S102 and S103 are executed again. On the other hand, when a positive determination is made in step S103, the process of step S104 is performed next. In step S104, the fuel addition from the fuel addition valve 4 is stopped. That is, the execution of the filter regeneration process is terminated.

Next, in step S105, the HC adhesion amount Qhc at the current SCRF 7 is calculated. The amount of HC adhering to the SCRF 7 per unit time and the amount of HC oxidized per unit time during execution of the filter regeneration process are the amount of fuel added from the fuel addition valve 4, the flow rate of exhaust, the temperature of the pre-stage catalyst 5, and It can be estimated based on the temperature of the SCRF 7 or the like. Then, by accumulating these values, the HC adhesion amount Qhc in SCRF 7 can be calculated.

Next, in step S106, an execution time ΔTp of the HC poisoning recovery process to be executed is set. Here, the execution time ΔTp of the HC poisoning recovery process is set based on the HC adhesion amount Qhc in SCRF7. That is, when the HC adhesion amount Qhc in SCRF 7 is large, the execution time ΔTp of the HC poisoning recovery process is set shorter than when the HC adhesion amount Qhc is small. The relationship between the HC adhesion amount Qhc in SCRF 7 and the execution time ΔTp of the HC poisoning recovery process is determined based on experiments and the like. The relationship between these values is stored in advance in the ECU 10 as a map or a function.

Next, in step S107, post injection in the internal combustion engine 1 is executed. That is, the HC poisoning recovery process is executed. In the HC poisoning recovery process, the temperature of the SCRF 7 is adjusted to the HC poisoning recovery temperature, which is the target temperature, by controlling the injection timing and the injection amount of the auxiliary fuel injection. The HC poisoning recovery temperature and the filter regeneration temperature may be the same temperature.

Next, in step S108, whether or not the time ΔTp set in step S106 has elapsed since the start of the post injection in the internal combustion engine 1, that is, the start of the HC poisoning recovery process. Determined. If a negative determination is made in step S108, the processes in steps S107 and S108 are executed again. On the other hand, if an affirmative determination is made in step S108, the process of step S109 is then executed. In step S109, the post injection is stopped. That is, the execution of the HC poisoning recovery process is terminated.

In the above flow, the execution time ΔTp of the HC poisoning recovery process is set based on the HC adhesion amount Qhc in SCRF7. Thereby, it is possible to suppress the HC poisoning recovery processing execution time ΔTp from becoming excessively long while sufficiently removing the HC adhering to the SCRF 7. For this reason, it is possible to suppress the deterioration of fuel consumption accompanying the execution of the HC poisoning recovery process.

In this embodiment, the HC poisoning recovery process may be executed without setting the execution time of the HC poisoning recovery process in advance. In this case, the residual amount of HC in SCRF 7 is estimated during the execution of the HC poisoning recovery process. Then, the execution of the HC poisoning recovery process may be terminated when the estimated residual HC amount is equal to or less than the predetermined residual amount. The amount of HC oxidation per unit time during execution of the HC poisoning recovery process can be estimated based on the flow rate of the exhaust gas, the temperature of the SCRF 7, and the like. Then, the HC residual amount in SCRF 7 can be calculated by subtracting the HC oxidation amount from the HC adhesion amount at the start of execution of the HC poisoning recovery process.

Also, the execution time of the HC poisoning recovery process may be set based on the execution time of the filter regeneration process. In this case, when the execution time of the filter regeneration process is short, the execution time of the HC poisoning recovery process is set shorter than when the execution time of the filter regeneration process is long. Also by this, it is possible to suppress excessively long execution time of the HC poisoning recovery process while sufficiently removing the HC adhering to the SCRF 7.

Also, the execution time of the HC poisoning recovery process may be a predetermined time. Even in this case, the HC adhering to the SCRF 7 can be removed by executing the filter regeneration process. However, from the viewpoint of suppressing deterioration in fuel consumption, it is preferable to change the execution time of the HC poisoning recovery process according to the HC adhesion amount in SCRF 7 or the execution time of the filter regeneration process as described above.

In this embodiment, the PM residual amount in SCRF 7 may be estimated during the filter regeneration process. Then, in step S103 of the above flow, when the estimated PM residual amount becomes equal to or smaller than the predetermined residual amount, it may be determined that the condition for ending the filter regeneration process is satisfied. The amount of PM oxidation per unit time during the execution of the filter regeneration process can be estimated based on the exhaust flow rate, the temperature of the SCRF 7, and the like. Then, the PM residual amount in SCRF 7 can be calculated by subtracting the PM oxidation amount from the PM deposition amount at the start of execution of the filter regeneration process.

In this case, the predetermined residual amount may be an amount larger than an amount at which it can be determined that substantially all of the oxidizable PM has been removed. By setting the predetermined residual amount to such an amount, it is possible to shorten the execution time of the filter regeneration process as compared with the case where PM is to be removed as much as possible. In the present embodiment, the temperature of the SCRF 7 is adjusted to a target temperature substantially the same as the target temperature in the filter regeneration process even during the execution of the HC poisoning recovery process. Therefore, even if PM remains in the SCRF 7 when the filter regeneration process is completed, the remaining PM can be oxidized and removed during the execution of the HC poisoning recovery process.

<Time chart>
FIG. 3 shows the temperature Tf of the SCRF 7, the temperature Tpc of the front catalyst 5, the fuel addition amount Fadd from the fuel addition valve 4, the internal combustion engine 1 when the filter regeneration process and the HC poisoning recovery process according to this embodiment are executed. 6 is a time chart showing changes in post injection amount Fpost at HC, HC adhesion amount Qhc at SCRF7, ammonia gas addition amount Aadd from the ammonia addition valve 6, and ammonia adsorption amount Qam at the SCR catalyst 7a. In FIG. 3, the horizontal axis represents time t. In FIG. 3, Tft represents the target temperature (filter regeneration temperature, HC poisoning recovery temperature) of SCRF 7 in the filter regeneration process and the HC poisoning recovery process.

In FIG. 3, the fuel addition from the fuel addition valve 4 is executed from time t0 to time t3. That is, the execution time of the filter regeneration process is from time t0 to t3. Therefore, during the period from time t0 to t3, the HC attachment amount Qhc in SCRF7 increases. During this time, the temperature Tf of the SCRF 7 gradually increases from the time t1 to the time t2, and the SCRF temperature Tf is maintained at the target temperature (filter regeneration temperature) Tft from the time t2 to the time t3.

Then, post injection in the internal combustion engine 1 is executed from time t3 to t4. That is, the period from time t3 to t4 is the execution time of the HC poisoning recovery process. During this time, the supply of new HC to the SCRF 7 is suppressed, and the temperature Tf of the SCRF 7 is maintained at the target temperature (HC poisoning recovery temperature). Therefore, during the period from time t3 to t4, the HC adhesion amount Qhc in SCRF7 decreases.

If the temperature Tf of the SCRF 7 reaches the target temperature (filter regeneration temperature, HC poisoning recovery temperature) Tft, it is difficult for ammonia to be adsorbed on the SCR catalyst 7a. Therefore, in the present embodiment, the addition of ammonia gas from the ammonia addition valve 6 is stopped during the execution of the filter regeneration process and the HC poisoning recovery process.

When the execution of the HC poisoning recovery process is completed at time t4, the addition of ammonia gas from the ammonia addition valve 6 is resumed. At this time, the HC adhering to the SCRF 7 by executing the filter regeneration process is removed by executing the HC poisoning recovery process. Therefore, the adsorption of ammonia in the SRC catalyst 7a is easily promoted.

Further, when the execution of the HC poisoning recovery process is completed at time t4, the temperature Tf of SCRF 7 (that is, the temperature of the SCR catalyst 7a) gradually decreases between time t4 and time t5. Accordingly, the amount of ammonia that can be adsorbed on the SCR catalyst 7a increases. Therefore, during the time t4 to t5, the ammonia gas addition amount Aadd from the ammonia addition valve 6 is gradually increased. Thereby, during the time t4 to t5, the ammonia adsorption amount Qam in the SCR catalyst 7a gradually increases.

[Modification]
Next, a modification of the present embodiment will be described. In this embodiment, after the completion of the filter regeneration process, that is, after the fuel addition from the fuel addition valve 4 is stopped, the temperature of the SCRF 7 is maintained at a temperature at which HC can be oxidized without performing the HC poisoning recovery process. If so, the HC attached to SCRF 7 is removed. Therefore, it is not always necessary to start the execution of the HC poisoning recovery process simultaneously with the end of the execution of the filter regeneration process.

Therefore, in this modification, the execution start time of the HC poisoning recovery process is determined based on the temperature of the SCRF 7 after the execution of the filter regeneration process is completed. FIG. 4 is a flowchart showing the flow of filter regeneration processing and HC poisoning recovery processing according to this modification. In this flow, processes other than step S205 are the same as those in the flowchart shown in FIG. Therefore, only the process of step S205 will be described, and the description of the process of other steps will be omitted. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10.

In this flow, the process of step S205 is executed after step S104. In step S205, it is determined whether or not the temperature of SCRF 7 has become equal to or lower than a predetermined processing start temperature Tf0. Here, the processing start temperature Tf0 is a temperature that is equal to or lower than a target temperature (filtering temperature) for the filter regeneration processing and is equal to or higher than a lower limit value of the temperature at which HC attached to the SCRF 7 can be oxidized. This processing start temperature Tf0 is determined in advance based on experiments and the like.

If a negative determination is made in step S104, the process of step S104 is executed again. On the other hand, if an affirmative determination is made in step S104, the process of step S105 is then executed.

In this case, in step S105, the amount of HC deposited in SCRF 7 at the current time is subtracted from the amount of HC deposited in SCRF 7 at the end of execution of the filter regeneration process to subtract the amount of HC oxidized after the completion of execution of the filter regeneration process. Is calculated.

According to this, compared with the case where the execution of the HC poisoning recovery process is started simultaneously with the end of the execution of the filter regeneration process, the amount of HC adhering to the SCRF 7 at the start of the execution of the HC poisoning recovery process is reduced. Therefore, the execution time ΔTp of the HC poisoning recovery process set in step S106 can be shortened. As a result, it becomes possible to further suppress the deterioration of fuel consumption accompanying the execution of the HC poisoning recovery process.

<Example 2>
The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that according to the first embodiment. Hereinafter, only differences from the first embodiment in the filter regeneration process and the HC poisoning recovery process according to the present embodiment will be described.

As described above, when the temperature of the SCRF 7 rises to the target temperature (filter regeneration temperature, HC poisoning recovery temperature), it is difficult for ammonia to be adsorbed on the SCR catalyst 7a. Therefore, in Example 1, the addition of ammonia gas from the ammonia addition valve 6 was stopped during the execution of the filter regeneration process and the HC poisoning recovery process. However, ammonia can be adsorbed on the SCR catalyst 7a until the temperature of the SCRF 7 reaches the target temperature during the filter regeneration process, that is, while the temperature of the SCRF 7 is lower than the target temperature. Therefore, in this embodiment, addition of ammonia gas from the ammonia addition valve 6 is executed until the temperature of the SCRF 7 reaches the target temperature even during execution of the filter regeneration process.

Thus, ammonia can be adsorbed on the ammonia adsorption sites in the SCR catalyst 7a even during the time until the temperature of the SCRF 7 reaches the target temperature during execution of the filter regeneration process. Therefore, the amount of HC adhering to SCRF 7 during the filter regeneration process can be suppressed. As a result, the amount of HC adhering to SCRF 7 at the end of execution of the filter regeneration process can be reduced.

Therefore, according to the present embodiment, it is possible to shorten the execution time of the HC poisoning recovery process compared to the case where the addition of ammonia gas from the ammonia addition valve 6 is stopped from the start of the execution of the filter regeneration process. Become. For this reason, it is possible to further suppress the deterioration of fuel consumption accompanying the execution of the HC poisoning recovery process.

[Flow of ammonia gas addition control]
FIG. 5 is a flowchart showing a flow of ammonia gas addition control during the execution of the filter regeneration process according to the present embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10.

In this flow, first, in step S301, it is determined whether or not the filter regeneration process is being executed. If a negative determination is made in step S301, the execution of this flow is temporarily terminated. On the other hand, if an affirmative determination is made in step S301, the process of step S302 is then executed.

In step S302, it is determined whether or not the temperature Tf of the SCRF 7 is lower than the target temperature Tft (filter regeneration temperature) Tft. If an affirmative determination is made in step S302, then the process of step S303 is executed. In step S303, an ammonia gas addition amount Add from the ammonia addition valve 6 is set. Here, the ammonia gas addition amount Add is set according to the temperature Tf of SCRF 7 (that is, the temperature of SCR catalyst 7a). That is, when the temperature Tf of the SCRF 7 is high, the ammonia addition amount Add is set smaller than when the temperature is low. The relationship between the ammonia addition amount Add and the temperature Tf of the SCRF 7 is determined based on experiments and the like. The relationship between these values is stored in advance in the ECU 10 as a map or a function.

Next, in step S304, addition of ammonia from the ammonia addition valve 6 is executed. At this time, the amount of ammonia added is adjusted to the amount set in step S303.

On the other hand, if a negative determination is made in step S302, that is, if the temperature of SCRF 7 has reached the target temperature Tft, the process of step S305 is then executed. In step S305, the addition of ammonia gas from the ammonia addition valve 6 is stopped.

According to the above flow, when adding ammonia gas from the ammonia addition valve 6 during execution of the filter regeneration process, the amount of ammonia gas added from the ammonia addition valve 6 gradually increases as the temperature of the SCRF 7 rises. Reduced to Thereby, it can suppress that an excessive amount of ammonia gas is supplied to SCRF7. Therefore, the ammonia outflow from SCRF 7 can be suppressed.

[Time chart]
FIG. 6 shows the temperature Tf of the SCRF 7, the temperature Tpc of the front catalyst 5, the fuel addition amount Fadd from the fuel addition valve 4, the internal combustion engine 1 when the filter regeneration process and the HC poisoning recovery process according to this embodiment are executed. 6 is a time chart showing changes in post injection amount Fpost at HC, HC adhesion amount Qhc at SCRF7, ammonia gas addition amount Aadd from the ammonia addition valve 6, and ammonia adsorption amount Qam at the SCR catalyst 7a. In FIG. 6, the horizontal axis represents time t. In FIG. 6, Tft represents the target temperature (filter regeneration temperature, HC poisoning recovery temperature) of SCRF 7 in the filter regeneration process and the HC poisoning recovery process. In FIG. 6, the solid line indicates the transition of each value according to the present embodiment, and the broken line indicates the transition of each value when the filter regeneration process and the HC poisoning recovery process according to the first embodiment are performed. Show.

In this embodiment, the addition of ammonia gas from the ammonia addition valve 6 is also executed during the time t0 to t2 during which the filter regeneration process is being executed. Then, during the time t1 to t2, the amount of ammonia gas added from the ammonia addition valve 6 is gradually reduced as the temperature of the SCRF 7 rises. As a result, at the time t2, the ammonia adsorption amount Qam in the SCR catalyst 7a becomes substantially zero.

However, during the period from time t0 to t2, ammonia is adsorbed at the ammonia adsorption site in the SCR catalyst 7a, so that HC hardly adheres to the SCRF 7. Therefore, the HC adhesion amount Qhc in the SCRF 7 at the time t3 when the execution of the filter regeneration process ends is smaller than that in the first embodiment. Therefore, the execution time of the HC poisoning recovery process (time from t3 to t4) can be shortened compared to the case of the first embodiment.

In the HC poisoning recovery process according to Examples 1 and 2, the SCRF 7 rises to a temperature at which PM oxidation is promoted, as in the filter regeneration process. However, when the temperature of the SCRF 7 is increased by increasing the temperature of the exhaust gas discharged from the internal combustion engine 1 as in the HC poisoning recovery process, the temperature of the SCRF 7 is set to the same temperature by supplying fuel to the upstream catalyst 5. Compared with the case where the fuel consumption is increased up to, the fuel consumption is increased. Therefore, removal of PM deposited on SCRF 7 is performed by filter regeneration processing in order to suppress deterioration of fuel consumption.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Fuel addition valve 5 ... Pre-stage catalyst 6 ... Ammonia addition valve 7 ... Filter (SCRF)
7a ・・ Selective reduction type NOx catalyst (SCR catalyst)
8... Rear stage catalyst 10 ..ECU
11. ・ Air flow meter 12 ・・ First exhaust temperature sensor 13 ・・ Second exhaust temperature sensor 14 ・・ Third exhaust temperature sensor

Claims

A pre-stage catalyst provided in the exhaust passage of the internal combustion engine and having an oxidation function;
A fuel supply device for supplying fuel to the upstream catalyst;
A filter that is provided in an exhaust passage downstream of the preceding catalyst and collects particulate matter in exhaust gas, and carries a selective reduction type NOx catalyst that reduces NOx in exhaust gas using ammonia as a reducing agent. When,
An ammonia supply device for supplying ammonia or an ammonia precursor to the filter;
A filter regeneration process execution unit for performing a filter regeneration process for increasing the temperature of the filter by supplying fuel from the fuel supply device to the upstream catalyst, thereby removing particulate matter deposited on the filter;
After the completion of the filter regeneration process by the filter regeneration process execution unit, the temperature of the filter is raised by raising the temperature of the exhaust discharged from the internal combustion engine, thereby removing the HC adhering to the filter. An exhaust purification system for an internal combustion engine, comprising: an HC poisoning recovery process execution unit that executes a poison recovery process.
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the HC poisoning recovery process is executed for a time corresponding to the amount of HC adhering to the filter at the start of execution of the HC poisoning recovery process.
The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the HC poisoning recovery process is executed for a time corresponding to the execution time of the filter regeneration process.
The ammonia or ammonia precursor in an amount corresponding to the temperature of the filter is supplied to the filter by the ammonia supply device until the temperature of the filter reaches a target temperature during the filter regeneration process. The exhaust gas purification system for an internal combustion engine according to any one of claims 3 to 4.